The present invention relates to an azo group-containing high-molecular weight compound.
Azo compounds have been widely used as a radical polymerization initiator for vinyl monomers.
The production of a block copolymer using a high-molecular weight azo compound has recently been proposed (for instance, Ueda and Nagai, "Kagaku to Kogyo (Osaka)", 60, 57 (1986)). Specifically, there has been proposed a process comprising carrying out first-stage polymerization under such conditions that a certain amount of azo groups are cleaved, by use of a linear high-molecular weight azo compound having a plurality of azo groups in the main chain which is obtained by alternating polycondensation of 4,4'-azobis(4-cyano-pentanoyl chloride) with a bifunctional compound such as hexamethylenediamine, for example, a compound represented by: ##STR1## wherein m is a natural number, and carrying out second-stage and subsequent polymerizations by utilizing the remaining azo groups. It has already been reported that this process permits efficient production of a block copolymer comprising poly(methyl methacrylate) moieties and poly(n-butyl acrylate) moieties (for instance, Ueda and Nagai "Kobunshi Ronbunshu", 44, 469, (1987)).
Such block copolymers can be utilized for various special purposes but in some cases, only block copolymers having a specific structure (for example, MNM type polymers containing a polymer segment M and a polymer segment N in the case of thermoplastic elastomers) are useful. Therefore, there is eagerly desired a process for producing a block copolymer having a controlled structure.
The polymerization method using a high-molecular weight azo compound of the above formula involves the following problem. Since the azo groups present in the main chain are equal in cleavability, the initiation point of polymerization is tend to be random even though controllable to a certain extent by the reaction conditions and the like. Consequently, there are obtained block copolymers of various and many types such as a so-called MN type, MNM type, and (MN).sub.n type. Thus, a block copolymer having a controlled structure cannot be efficiently obtained by a one-step reaction.